Distribution Of Nb Research Articles

Comprehensive investigation of the role of Nb on the oxidation kinetics of Zr-Nb alloys

Waterside corrosion of zirconium alloys is currently the life-limiting degradation mechanism of fuel elements in pressurized-water reactor (PWR) systems. Today, PWRs use Zr-Nb fuel cladding designed to limit oxidation and hydrogen pickup. However, oxidation kinetics of Zr-Nb alloys can vary substantially depending on the Nb content and distribution, even in alloys of the same composition but different heat treatments. To elucidate the role of Nb on Zr-Nb oxidation kinetics and improve the fundamental understanding of Zr-Nb corrosion, nano-beam X-ray absorption near-edge spectroscopy (XANES), transmission electron microscopy (TEM), and application of the Coupled-Current Charge-Compensation (C4) Model have been performed in concert.

Distribution of Nb and Ce between Two Immiscible Melts in the System CePO4–SiO2–NaF–Fe2O3–Nb2O5

The CePO 4 – SiO 2 – NaF – Fe 2 O 3 –Nb 2 O 5 system is characterized by a wide area of two immiscible melts. As the temperature in the system increases, the region of incompressibility of melts increases. Mutual solubility of immiscible melts is low and is 3–5% by weight. The decrease in the melting point of the components is due to chemical reactions between SiO 2 and NaF and between cerium orthophosphate and sodium fluoride. New previously unknown phases were established in the system: double salt of cerium and sodium, fluoride phosphate of cerium and sodium and phase with high content of niobium. Niobium oxide is distributed between the silicate melt, silicate balls, which is part of the phosphate fluoride melt and a phase with a high content of niobium. Cerium is concentrated in the phosphate-salt melt, where it is found in the double salt of cerium and sodium and the fluoride phosphate of cerium and sodium.

Niobium incorporated WO3 nanotriangles: Band edge insights and improved photoelectrochemical water splitting activity

In this work, a facile hydrothermal method is proposed to fabricate Nb-doped WO3 nanotriangle thin films, and their band edge properties and photoelectrochemical water splitting activity were explored. The process of doping and thin film formation was simultaneously achieved in a single step hydrothermal condensation of peroxopolytungstic acid solution containing Nb precursor. The crystallographic study reveals that doping of Nb into WO3 lattice obstructs the reconstructive transformation of orthorhombic WO3·0.33H2O during annealing consequently producing hexagonal phase instead of the monoclinic phase. The insertion of Nb causes the increase in band gap and induces oxygen vacancies in WO3. Uniform distribution of Nb in WO3 was observed containing majorly Nb5+ valence and a small amount of Nb4+ state. PEC characterization showed the increase in photocurrent, (at AM 1.5G illumination) incident photon to current and photoconversion efficiency values of WO3 upon Nb doping. Band edge analysis revealed that both conduction and valence band edge of WO3 show downward shift towards higher potential vs. RHE whereas the Fermi level show upward shift as a result of Nb doping.

PECULIARITIES OF DISTRIBUTION AND COMPOSITION OF BETAFITE FROM DIFFERENT FORMATIONS OF THE ALDAN SHIELD (SAKHA-YAKUTIA)

Character of Nb and Ta distribution in the different geological formations of the Aldan Shield are given in this article. To get idea about betafite from different endogenic etalon formations the authors analyzed its well known locations in the pegmatites, skarns, carbonatites, metasomatites and late veins segregations. Geological setting and mineralogical composition of the apatite-bearing rocks from the Aldan Shield are described, and the most significant in scale metamorphosed carbonate and silicate varieties among them have been distinguished. Apatite mineralization in magnesium skarns and metasomatites is developed locally. Titanite and betafite are the main concentrators of Nb and Ta and apatite is typical accompanying mineral in the studied rocks. Betafite was detected in the pegmatite bodies from magnesium skarns and metasomatites of the Shield with irregular distribution within rocks rich and poor in apatite, but was not found in the most developed apatite-carbonate rocks which are regarded as ores of the Seligdar type, so it cannot be mineralogical indicator for this type of ores. Late carbonate generations are significantly enriched in light carbon and oxygen isotopes in contrast to positive δ13Ñ values in apatitecarbonate bodies of the Seligdar deposit and its family and the highest δ18Î values. We used these indicators to distinguish origin of the rocks with various carbonate generations, which have different amounts of betafite. Appearance of betafite is determined by primary composition of the initial rocks. Chemical composition of betafites from the skarns and metasomatites is similar, but with local variations. The most significant feature of the mineral composition is very low Ta content. Titanite is characterized by variable amounts of Nb and Ta in scale of sectors as well as within separate grains.

Тантало-ниобаты в породах федотовской свиты верхнего рифея (Средний Урал)

The petrographic peculiarities of the Fedotovskaya Suite of the Upper Riphean in the western slope of the Middle Urals are considered. The mineral varieties of tantal-niobium components (ilmenorutile, tantalorutile, yttrocolumbite, polycrase) and geochemical regularities in distribution of niobium concentrations in well sections are described. The connection of Nb high concentrations with metariolite and metabasalt layers is established. The rhythmical distribution of Nb along the carbon-serisite-quartz schist section with alternation of high and low concentrations is discovered. The results of study may be used for solution of theoretical problems of the black shales formation, as well as for designing the prospecting work on complex placers.

3D Modeling of the Epembe (Namibia) Nb-Ta-P-(LREE) Carbonatite Deposit: New Insights into Geometry Related to Rare Metal Enrichment

Geological 3D modeling delivers essential information on the distribution of enrichment zones and structures in (complex) mineral deposits and fosters a better guidance to subsequent exploration stages. The Paleoproterozoic Epembe carbonatite complex showcases the close relation between enrichment of specific elements (Nb, Ta, P, Total Rare Earth Element (TREE) + Y) and shear zones by structural modeling combined with geochemical interpolation. Three-dimensional fault surfaces based on structural field observations, geological maps, cross-sections, and drillhole data are visualized. The model shows a complex, dextral transpressive fault system. Three-dimensional interpolation of geochemical data demonstrates enrichment of Nb, Ta, P, and TREE + Y in small, isolated, lens-shaped, high-grade zones in close spatial distance to faults. Based on various indicators (e.g., oscillating variograms, monazite rims around the apatite) and field evidence, we see evidence for enrichment during hydrothermal (re-)mobilization rather than due to magmatic differentiation related to the formation of the alkaline system. This is further supported by geostatistical analysis of the three-dimensional distribution of Nb, Ta, P, and Light Rare Earth Elements (LREE) with respect to discrete shear zones.

Episodic Nb–Ta mineralisation in South China: Constraints from in situ LA–ICP–MS columbite-tantalite U–Pb dating

South China hosts many Nb–Ta deposits that show evidence for episodic mineralization, which were generated during the emplacement of composite granites. To constrain the spatio-temporal distribution of Nb–Ta mineralisation in the region and to identify future targets for mineral exploration, we used in situ laser ablation-inductively coupled plasma-mass spectroscopy to date 23 columbite-tantalite group mineral (CGM) samples from 14 Nb–Ta deposits. Our CGM U–Pb data, supplemented by previous results, reveal five distinct Nb–Ta mineralisation events in South China as follows: (1) Late Silurian–Middle Devonian (ca. 424–391 Ma; e.g., the Xigang and Nanping deposits in eastern Jiangxi and western Fujian Provinces); (2) Triassic (ca. 248–204 Ma; e.g., the Houxi, Cunxin, Dongtounan, Shenkeng, Limu and Gaoling deposits in western Guangdong Province and northeastern Guangxi Zhuang Autonomous Region; (3) Late Jurassic (ca. 160–150 Ma; e.g., the Gedongping, Yichun, Laiziling, Jianfengling and Jinzhulong deposits in Guangxi, Jiangxi and Hunan Provinces); (4) Early Cretaceous (ca. 130 Ma; e.g., the Huangshan and Songshugang deposits in northeastern Jiangxi province); and (5) Late Cretaceous (ca. 90 Ma; e.g., the Jiepailing deposit, located along the boundary between Hunan and Jiangxi Provinces). We show that Nb–Ta mineralisation in South China was controlled by multiple tectono-magmatic events. Our CGM samples yielded Caledonian (ca. 424–391 Ma), early Indosinian (ca. 248 Ma) and late Yanshanian (ca. 130 Ma) ages, indicating that Nb–Ta mineralisation was abundant during these times and should form the focus for future studies of mineralisation in the region. Early Triassic granite in the Guangning Nb–Ta metallogenic district in western Guangdong Province, Indosinian and early Yanshannian granites in the Miao’ershan–Yuechengling batholith in northeastern Guangxi, and the Late Cretaceous Lingshan batholith in northern Jiangxi Province are identified as targets for future Nb–Ta exploration.

Geochemistry and grain size distribution of surface sediments of a large semi-enclosed lagoon connected to the western Bay of Bengal

Batticaloa is a large (135.5 km2), semi-enclosed, micro-tidal lagoon that formed by barrier deposits in eastern Sri Lanka and has a unique geographic position due to its tropical monsoonal climate and absence of tectonics. The recent soft bottom sediments of Batticaloa lagoon were studied on the basis of geochemistry and grain size distribution in order to interpret their characteristics and provenance. Poor to moderately sorted medium sands are the dominant sedimentary deposits for the lagoon; therefore, a medium energy condition is suggested for sediment deposition. The average silt and clay fraction of the lagoon sediments is less than 3%, indicating medium or high energy flows. Coarser deposits are restricted to channel and lagoon mouths. The scatter plots of Nb, Zr, Cr and Sc vs. Th and Cr/V vs. Y/Ni show a felsic provenance for the sediments. The normalized diagrams of major element oxides and trace elements for the regional rocks (Vijayan Complex of Sri Lanka) indicate high country rock influence for the sedimentation for the semi-enclosed setting. The enrichment and distribution of Zr, Th, Nb, Cr and TiO2 suggest the possibility of mineral sands that are fractionated with hydrodynamic setting of the lagoon.

Effect of Silicate Matter on Pyrochlore Solubility in Fluoride Solutions at Т = 550–850°C, Р = 50–100 MPa (Experimental Studies)

The experimental results of natural pyrochlore behavior in KF solutions in the presence of quartz at 550–850°C and 50–100 MPa are presented. It is shown that silicate matter (quartz) exerts a significant effect on pyrochlore solubility in aqueous solutions of fluorides of alkaline metals under hydrothermal conditions. This study of the fluid inclusions has revealed the occurrence of reactions of high-temperature hydrolysis of KF under the experimental conditions: KF + H2O = KOH + HF; in which case, the interaction with quartz SiO2 + 2KOH = K2SiO3 + H2O is followed by the formation of a silicate glass phase (an aqueous solution–melt). This phase of alkaline glass is a Nb concentrator (Nb2O5 up to 16 wt %). The coefficient of Nb distribution between the glass and the fluid is ≈500 (in favor of the glass). It is determined that the phase of the silicate solution–melt can serve as an effective concentrator of the ore component (Nb) at the last lowtemperature stages of crystallization of rare-metal granites.

Distribution of zirconium, hafnium, niobium and tantalum in the North Atlantic Ocean, northeastern Indian Ocean and its adjacent seas

The two pairs of geochemical twins, Zr–Hf and Nb–Ta, have similar chemical properties, leading to their limited fractionation throughout the igneous processes and thus useful and widely used to elucidate rock and mineral formation. In contrast to the analysis of solid samples (e.g. igneous rocks), however, reports of these elements from aquatic samples (e.g. seawater) are very limited due to difficulties in analyzing their very low concentrations in seawater compared to those in solid samples (up to 6 orders of magnitude different). Recent developments of clean sampling techniques coupled with pre-concentration and ICP-MS determination have made trace elements analysis in seawater reliable. Here we report the first vertical distribution of dissolved Zr, Hf, Nb and Ta in the Indian Ocean in addition to those in the Atlantic Ocean, Andaman Sea and Gulf of Thailand. In the Atlantic and northeastern Indian Ocean, Zr, Hf, Nb and Ta show surface depletion and deep water enrichment. The average deepwater Zr/Hf molar ratios in the western North Atlantic, eastern North Atlantic and northeastern Indian Ocean were 270, 315 and 280, respectively. Compared to North Pacific Ocean Zr/Hf ratios of ~500, strong intra- and inter-ocean fractionation, a term that describe a difference between concentration of trace metals in deep Atlantic and deep Pacific seawater, is observed to occur in the global ocean. However, the inter-ocean fractionation of Nb/Ta is weaker due to a more uniform distribution of Nb and Ta in seawater. In contrast to open ocean seawater, Zr, Hf, Nb and Ta concentration at stations close to the continent in the Andaman Sea and Gulf of Thailand were highest in surface water decreasing through deep water, with Zr/Hf and Nb/Ta closer to continental crust ratios indicating significant terrestrial inputs of these elements to seawater. Results suggest that, in spite of the similar chemical properties of these geochemical twin pairs generating coherent fractionation in igneous rocks, strong fractionations of Zr–Hf and Nb–Ta takes place in aquatic environments such as seawater.

Microstructural characterization of laser metal powder deposited Alloy 718

A microstructural study of Laser Metal Powder Deposition (LMPD) of Alloy 718, using a low (40 J/mm) and high (100 J/mm) heat inputs (HIs) was performed. The microstructure was characterized in as-deposited condition as well as after a standard heat-treatment, using optical microscope (OM), scanning electron microscope (SEM) and Transmission Electron Microscope (TEM). Laves, MC-carbides, γ′ and γ″ are observed in the interdendritic areas of both conditions. However, the dendritic core only consists of γ-matrix. The high HI condition shows a slightly larger Primary Dendrite Arm Spacing (PDAS) as compared to the low HI condition. Additionally, the particle size of the Nb-rich constituents in the interdendritic regions (Laves-phase and Niobium carbide) is larger in the high HI sample. After heat-treatment, the Laves phase dissolves and is replaced by δ-phase in the interdendritic regions, while γ′, γ″ and MC-carbide remain in the interdendritic regions. However, the γ″ precipitates seems to be less developed in the dendritic core as compared to the interdendritic regions, especially in the high HI sample. This can be attributed to a heterogeneous distribution of Nb in the microstructure, with a lower Nb content in the dendritic core as compared to close to the interdendritic regions.

The Application of 40Ti-35Ni-25Nb Filler Foil in Brazing Commercially Pure Titanium

The clad ternary 40Ti-35Ni-25Nb (wt %) foil has been applied in brazing commercially pure titanium (CP-Ti). The wavelength dispersive spectroscope (WDS) was utilized for quantitative chemical analyses of various phases/structures, and electron back scattered diffraction (EBSD) was used for crystallographic analyses in the brazed joint. The microstructure of brazed joint relies on the Nb and Ni distributions across the joint. For the β-Ti alloyed with high Nb and low Ni contents, the brazed zone (BZ), consisting of the stabilized β-Ti at room temperature. In contrast, eutectoid decomposition of the β-Ti into Ti2Ni and α-Ti is widely observed in the transition zone (TZ) of the joint. Although average shear strengths of joints brazed at different temperatures are approximately the same level, their standard deviations decreased with increasing the brazing temperature. The presence of inherent brittle Ti2Ni intermetallics results in higher standard deviation in shear test. Because the Ni content is lowered in TZ at a higher brazing temperature, the amount of eutectoid is decreased in TZ. The fracture location is changed from TZ into BZ mixed with α and β-Ti.

Mechanical Properties of a Newly Additive Manufactured Implant Material Based on Ti-42Nb.

The application of Ti-6Al-4V alloy or commercially pure titanium for additive manufacturing enables the fabrication of complex structural implants and patient-specific implant geometries. However, the difference in Young’s modulus of α + β-phase Ti alloys compared to the human bone promotes stress-shielding effects in the implant–bone interphase. The aim of the present study is the mechanical characterization of a new pre-alloyed β-phase Ti-42Nb alloy for application in additive manufacturing. The present investigation focuses on the mechanical properties of SLM-printed Ti-42Nb alloy in tensile and compression tests. In addition, the raw Ti-42Nb powder, the microstructure of the specimens prior to and after compression tests, as well as the fracture occurring in tensile tests are characterized by means of the SEM/EDX analysis. The Ti-42Nb raw powder exhibits a dendrite-like Ti-structure, which is melted layer-by-layer into a microstructure with a very homogeneous distribution of Nb and Ti during the SLM process. Tensile tests display Young’s modulus of 60.51 ± 3.92 GPa and an ultimate tensile strength of 683.17 ± 16.67 MPa, whereas, under a compressive load, a compressive strength of 1330.74 ± 53.45 MPa is observed. The combination of high mechanical strength and low elastic modulus makes Ti-42Nb an interesting material for orthopedic and dental implants. The spherical shape of the pre-alloyed material additionally allows for application in metal 3D printing, enabling the fabrication of patient-specific structural implants.

Nonlinear behavior of structural and luminescent properties in Gd(NbxTa1-x)O4 mixed crystals

Ceramic samples of gadolinium tantalo-niobate mixed crystals were obtained by the solid-state technique. The dependence of luminescence properties on the Nb/Ta ratio in the Gd(NbxTa1-x)O4 system is studied in the 5–450 K temperature range, including thermostimulated luminescence curves in the series of solid solutions. The relation of nonlinear behavior of light output with x variation to non-homogeneous distribution of Nb and Ta in solid solutions is discussed.

Electron localization in niobium doped CaMnO3 due to the energy difference of electronic states of Mn and Nb.

The electron localization in Nb-doped CaMnO3 is analyzed in terms of the space and energy distribution of electronic states employing first-principles calculations. The energy difference of Mn 3d states and Nb 4d states makes NbO6 octahedra impede electrical conduction, so the random distribution of Nb in lattices leads to the localization of electrons near the bottom of the conduction bands. Therefore, although more carriers are introduced when Nb-doping content increases, both the electrical conductivity and absolute thermopower decrease in Nb heavy doped CaMnO3. The calculated transport properties agree well with the experimental data, supporting the analysis of localization.

Pinning effect of strain induced Nb(C,N) on case hardening steel under warm forging conditions

The effectiveness of Nb in retarding dynamic recrystallization (DRX) during warm forging process (700∘C–900 ∘C) and its dependence on the process parameters(ε,ε˙,T), which are the definers of formation conditions and morphology of the strain induced Nb(C,N), were studied. Due to its capacity of interaction with the austenite phase through solute drag and precipitate pinning effects, Nb is an important variable in the production of high-strength low-alloy steel (HSLA). However, the effectiveness of Nb as austenite conditioner is strictly dependent on its correct manipulation within each manufacturing step of finished or semi-finished products. Computer simulation of the precipitation kinetics of a forging steel 0.03wt. pct. Nb was performed in order to design a thermomechanical processing route based on the time-temperature-precipitation diagram (TTP), thereby ensuring high precipitate phase fraction in short processing time. Characterization of the steel mechanical behavior and its dependence with the formation of Nb(C,N) was done through flow stress curves analysis, the relaxation rate for the microalloyed steel is remarkably lower than for the Nb free steel being a typical stress plateau (carbonitride formation) and a peak stress (recrystallization) respectively observed. Transmission electron microscopy (TEM) was performed in order to characterize the distribution, geometry and dimension of Nb(C,N) generated by different processing routes at different process stages. The solubilization capacity of the adopted and computational designed austenitizing process was also experimentally analyzed. The energy-dispersive X-ray spectroscopy (EDX) method was used in the characterization of the precipitates chemical composition, allowing the identification of Ti-rich precipitation remnants of the austenitizing process and the absence of the element in the Nb(C,N) formed during deformation (strain induced precipitates). The strain, strain rate, temperature and isothermal holding time contribution upon the formation of precipitates were evaluated separately which reveals that it is so important as the processing temperature, the strain rate regime play decisive role in the formation of the particles. In addition, the strain rate dependency of strain induced Nb-precipitates formation at optimal processing temperature was indirectly confirmed by the capacity of the formed precipitates in hinder the static recrystallization (SRX) progress under relaxation tests.The strain induced precipitation formed at optimal processing conditions have circular geometry and size below 10nm, causing high precipitate pinning effect observed in the conditioning of austenite phase by hindering the DRX under warm forging condition.

Developing accident prediction model for railway level crossings

Railway level crossing (LX) safety continues to be one of the most critical issues for railways, despite an ever-increasing focus on improving design and application practices. Accidents at European LXs account for about one-third of the entire railway accidents and result in more than 300 deaths every year in Europe. Due to the non-deterministic causes, the complex operation background and the lack of thorough statistical analysis based on accident/incident data, the risk assessment of LXs remains a challenging task. In the present paper, some LX accident prediction models are developed. Such models allow for highlighting the influence of the main impacting parameters, i.e., the average daily road traffic, the average daily railway traffic, the annual road accidents, the vertical road profile, the horizontal road alignment, the road width, the crossing length, the railway speed limit and the geographic region. The Ordinary Least-Squares (OLS) and Nonlinear Least-Squares (NLS) methods are employed to estimate the respective coefficients of variables in the prediction models, based on the LX accident/incident data. The validation and comparison process is performed through statistical means to examine how well the estimation of the models fits the reality. The outcomes of validation and comparison attest that the improved accident prediction model has statistic-based approbatory quality. Moreover, the improved accident prediction model combined with the NB distribution shows relatively high predictive accuracy of the probability of accident occurrence.

Elemental distribution in the martensite–austenite constituent in intercritically reheated coarse-grained heat-affected zone of a high-strength pipeline steel

We have studied here the distribution of carbon and alloying elements in the martensite-austenite (M-A) constituent in intercritically reheated coarse-grained heat-affected zone (ICCGHAZ) of a high-strength pipeline steel using atom probe tomography (APT). Notable enrichment of C (0.49wt%) and Mn (2.32wt%) was observed within the M-A constituent, which induced the formation of lath martensite and deteriorated the toughness. Elemental segregation in the interfacial region between M-A constituent and matrix may contribute to the debonding mechanism of M-A constituent and assist nucleation of cleavage cracks. Distribution of solute Nb indicated no apparent difference between the matrix and M-A constituent.

Environmental impact of disposal of coal mining wastes on soils and plants in Rostov Oblast, Russia

Underground coal mining in Southern European Russia leads to soil cover destruction in areas directly occupied by spoil tips and rock dumps located nearby. Coal producing areas in Rostov Oblast were selected for a detailed consideration. Soil samples were taken from the uppermost horizons: a layer of 0–10cm of spoil tips and surrounding areas, as well as from 1.5m depth vertical soil profiles. The soil samples were analysed for mineral composition, particle-size distribution and gross contents of Cu, Zn, Pb, Ag, Sn, Mo, Ba, Co, Ni, Mn, Ti, V, Cr, Ga, P, Li, Sr, Y, Yb, Nb, Sc and Zr, using emission spectral analysis. The plant species of mining influenced areas were described. The process of Technosol formation at the waste sites was considered separately. Soils have not yet formed as a result of a self-restoration on the spoil tips aged more than 50years and burnt-out decades ago. A vegetation cover, which emerged during this time range, practically does not support the progress of any considerable soil-forming process. The ponds formed by the flooding of burning spoil tips, do not give the possibility for the formation of soils and hardly contribute to plant growth. The surface layers of spoil tips at all stages of their development are different from the surrounding steppe soils in geochemical characteristics and mineralogical composition. The atmospheric and water inflow of material from spoil tips changes (in the cases studied - worsens) a state of steppe soils within a radius of 1 km, and leads to the increase of heavy metal content in these soils.

Nanoscale analysis of structural and chemical changes in aged hybrid Pt/NbO x /C fuel cell catalysts

We characterize the structural and chemical changes that take place in an electrochemically tested proton-exchange fuel cell cathode material composed of platinum nanoparticles on a niobium oxide-carbon black hybrid support. Two hybrid catalysts with different niobium oxide content (5 wt% and 12 wt%) are compared at the beginning and end of potential cycling. We observe an overall increase in the particle size of the hybrid catalysts after potential cycling, mediated by Ostwald ripening process. The general nanostructure of the catalysts was composed of small Pt-rich particles that were linked to niobium oxide particles. Nanoscale and microscale spectroscopy of the pristine materials reveals several co-existing oxidized forms of niobium (5+, 4+, 2+) in the systems; the most predominant being Nb(V). The study of the energy loss near-edge structure of the Niobium L2,3 edge of catalysts after being subjected to accelerated stress test (AST) potential cycles provides clues on the evolution of niobium oxides (NbOx), in which the relative distribution of Nb(V) decreases, while the number of Nb particles in lower oxidation states slightly increases. Furthermore, energy-dispersive spectroscopy reveals that the content of Nb decreased after cycling, implying that the loss of NbOx eventually altered the fraction of linked Pt-NbOx sites. The observed nanoscale catalyst changes and the presence of the NbOx may have important implications for developing an alternative design for improved hybrid catalyst materials.